The research reported here deals with the effects of mood states on the behavior and perceptions of participants in a brief "get acquainted" interaction. In two related experiments, either a happy or a sad mood was induced in one member of a dyad by having that person describe a recent experience that had made him or her either extremely happy or extremely sad. The other member of each dyad was in a neutral mood. Dyads interacted (to "get acquainted") for ten minutes. Prior to the interaction, participants reported own mood and their expectations about partner's mood and about the interaction. After the interaction, they reported their perceptions of various features of the interaction, including their own and their partner's moods. Observers rated the levels of positive and negative affect displayed in participants' nonverbal behavior during the interaction.Initially, mood was expected to have positive (that is, mood congruent) effects on each of four sets of dependent variables measures: Expectations about partner and about the interaction; perceptions of own and partner's mood; judgments of partner's interpersonal behavior; and nonverbal behavior during the interaction. Results of the first study contradicted many of those predictions. They showed, instead, a negative (mood contrasting) effect for expectations about partners' mood. Also, nonverbal behavior that seemed more related to those expectations about partner's mood than to participants' own mood.These findings guided the design of a second study using the same mood induction paradigm, but that also independently manipulated expectations for partner's mood. Interactive effects of mood and expectation for partner's mood were found. Participants made more favorable judgments of their partner and exhibited more positive nonverbal behavior when they expected congruence between their own and their partner's mood for both positive and negative mood states. These findings are interpreted in relation to several theoretical conceptions: anchoring (Upshaw, 1969), social comparison theory (Festinger, 1950); and the Byrne-Clore similarity-attraction hypothesis (Byrne, 1969; Byrne & Clore, 1967).